In the field of graphic arts, a system for forming an image having a photographic characteristic of super high contrast (especially .gamma. of 10 or more) is required for enabling reproduction of a continuous resolution image through a half-tone image or reproduction of a line original image.
As a process for obtaining photographic characteristics of high contrast image, a lith developing method utilizing what is called an "infectious developing effect" has been used for a long time, but it has the disadvantage that the developer is unstable and, thus, it is difficult to be used.
On the other hand, processes for obtaining a high contrast image utilizing a more stable developer are disclosed in, for example, U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,221,857, 4,332,878, 4,634,661, 4,618,574, 4,269,922, 5,650,746, and 4,681,836.
These image forming systems are those in which a surface latent image type silver halide photographic material to which a hydrazine derivative is added is processed with a stable MQ developer (a developer containing hydroquinone and p-aminophenols in combination) or PQ developer (a developer containing hydroquinone and 1-phenyl-3-pyrazolidones in combination) having a pH value of from 11 to 12.3 to obtain a super high contrast negative image having a .gamma. value exceeding 10. According to these processes, because photographic characteristics of super high contrast and high sensitivity are obtained and a sulfite is allowed to be added to a developer in a high concentration, the stability of the developer to air oxidation is markedly improved in comparison with the conventional lith developer.
With regard to a photographic material for light room developing, which is used in assembly processes and dot-to-dot working operations, for example, in the case where the superimposition dot-to-dot working operation between a half-tone dot text and line original text is attempted to be carried out faithfully to the texts, a process for forming an image having super high contrast is required. For this purpose, the above-mentioned image forming systems using a hydrazine derivative is effective, and the typical application examples are disclosed in JP-A-62-640 (the term "JP-A" used herein means an "unexamined published Japanese patent application"), JP-AT-62-235938, JP-A-62-235939, JP-A-63-104046, JP-A-63-103235, JPA-63-296031, JP-A-63-314541, and JP-A-64-13545.
U.S. Pat. Nos. 4,998,604 and 4,994,365 disclose a hydrazine compound having ethylene oxide repeating units and a hydrazine compound having a pyridinium group. However, as is clear from examples described therein, high contrast is not yet sufficient, and it is difficult to obtain a high contrast and a necessary D.sub.max value under the practical developing conditions.
Moreover, in the high contrast systems using a hydrazine compound, there is a high tendency of bringing about the phenomenon of enlargement of the image, causing the problem that the reproduced half-tone image area becomes narrow.
On the other hand, it has been known that endiols such as ascorbic acid function as the main developing agent, and they become the focus of attention as the main developing agent having no problem in terms of ecology and toxicology. For example, U.S. Pat. Nos. 2,688,549 and 3,826,654 disclose that an image can be formed under a strong alkaline condition of a pH value of 12 or more. However, no high contrast image can be obtained in these image forming processes.
Several attempts have been made to increase the contrast in the developing system using ascorbic acid. For example, Zwicky discloses that in the case of using ascorbic acid as a sole main developing agent, a type of lith effect is expressed (J. Phot. Sc. Vol. 27, p. 185 (1979)), but the system using ascorbic acid has a low contrast in comparison with a hydroquinone-containing system. U.S. Pat. No. 1,896,022 and JPB-49-46939 (the term "JP-B" used herein means an "examined Japanese patent publication") disclose a system using a bisquaternary ammonium salt and ascorbic acid in combination, but even though the system has a developing acceleration effect, it has little effect for increasing contrast. JP-A-3-249756 and JP-A-4-32838 also describe the combination effect of use of ascorbic acid and a quaternary salt, but the resultant image has insufficient contrast. Furthermore, according to JP-A-5-88306, a high contrast can be obtained by using ascorbic acid as a sole main developing agent and keeping the pH value at 12.0 or more, but this system has a problem in terms of stability of the developer.
U.S. Pat. No. 3,730,727 discloses an example where a special developer comprising ascorbic acid and a hydrazine derivative as main ingredients can be used to obtain a developed system having a high sensitivity and low stain and fogging, but does not disclose enhancement of contrast.
It has been known that a photographic material containing hydrazine is processed with an ascorbic acid developer, and it is disclosed in, for example, U.S. Pat. No. 5,236,816, and WO 93/11456. In each case, sufficient contrast cannot be obtained. In the case of WO 93/11456, although high contrast is obtained-by incorporating an amine compound into a developer, it is not preferable in terms of environment. It is, therefore, desired to develop a developing process which gives a high contrast image using ascorbic acid, which is preferred in terms of toxicology, as a main developing agent.
As described above, the system for forming a super high contrast image using a hydrazine derivative is a system using a dihydroxybenzene compound such as hydroquinone, and has several drawbacks from the ecological and toxicological viewpoints. For example, hydroquinone, which has the effect of bringing about an allergy, is an undesirable component, and 1-phenyl-3-pyrazolidones has poor biodegradability. Moreover, a highly concentrated sulfite has a high COD (chemical oxide demand). Furthermore, amines as described in U.S. Pat. No. 4,975,354 are usually used in such an image forming system, but it is not preferable in terms of toxicity and volatility.